An experimental and theoretical study is proposed to investigate the parameters affecting hygroscopic aerosol movement and deposition in the bronchial airways. The experimental study consists of mechanically ventilating eviscerated dog lungs, including the trachea and larynx, with dyed hygroscopic monodisperse aerosols of known particle size, temperature and gas phase humidity. The location and amount of aerosol deposition will then be determined by dissection of the lungs and examination of dyed areas of the bronchial tree both macroscopically and microscopically. Eviscerated human lungs will be used as these become available. The theoretical phase of the study, which will be carried on simultaneously, involves the solution of coupled heat and mass transfer equations describing gas and liquid particle motion, and deposition of aerosol particles in the airways. These equations will be solved numerically to obtain a predition of location and amount of aerosol deposition in the bronchial tree as a function of the inlet properties of the aerosol. Th results of the experiments and theory will be combined and used to suggest methods of generating and administering medical hygroscopic aerosols such that deposition occurs in a desired location and amount in the lung.